The invention relates to a voltage generating circuit and to a voltage stabilized supply device including such a circuit.
At the present time, numerous voltage generating circuits are known. One of the problems that they have to solve is that of outputting a voltage level that is relatively stable or, at the very least, one that does not exceed a given maximum value, while the voltage level input to the circuit can vary, either above or below a nominal supply voltage.
To solve this problem, it has already been suggested to use components such as Zener diodes shunt connected at the input to the circuit in order to limit the voltage to a given level, in the event of the nominal voltage being exceeded. Furthermore, in order to protect the components present downstream, only a fraction of the voltage input to the circuit is used to generate the output voltage.
It will be appreciated, nonetheless that, with such a solution, the means used to achieve the desired output voltage level have to be over-dimensioned in relation to the means that it would have sufficed to use if all of the input voltage, and not just a fraction thereof, had been used. In the case of charge pump circuits, for example, it is necessary to increase the number of charge stages of the pump or pumps.
As a corollary, in circuits having the same characteristics, the response times to obtain the same output voltage level are longer for a circuit using only a fraction of the input voltage and not its totality. This will apply, in particular, to charge pump circuits having the same number of charge stages but using, or not using, all of the circuit input voltage.
The object of the present invention is to provide a voltage generating circuit and a voltage stabilized supply device including such a circuit that overcome the aforementioned drawbacks and that make it possible to avoid having to over-dimension the means used to obtain at the output the desired voltage level, that is to say, for example, that make it possible to reduce the number of charge stages of the charge pumps, in the event of such components being used.
A further object of the present invention is to provide a voltage generating circuit and a voltage stabilized supply device using such a circuit that make it possible to reduce the start-up times.
Another object of the present invention is to provide a voltage generating circuit and a stabilized voltage supply device including such a circuit that afford protection in the event of a voltage level exceeding the nominal voltage being present at the input.
Further objects and advantages of the invention will emerge in the course of the following description, which is given only by way of illustration and is not intended to limit same.
The invention relates firstly to a voltage generating circuit having:
a voltage input;
voltage boosting means, having an input and an output;
means for varying the voltage supply level of the input to the said boosting means from the said voltage input of the circuit, capable, on one hand, in a first state, of permitting the application, at the input to the said boosting means, of a fraction, that is possibly limited, of the voltage input to the circuit and, in a second state, of increasing the level of voltage applied to the said input to the boosting means and, on the other hand, of permitting the change-over from the said first to the said second state according to a triggering signal, obtained by feedback of the output voltage from the said boosting means to the said means for varying the voltage level, so as to optimize the production at the output from the said voltage boosting means of the desired voltage level.
The invention also relates to a voltage stabilized supply device including such a circuit.